External Power Supply for Solar Garden Light

Discussion in 'The Projects Forum' started by Artbuc1, Jan 3, 2016.

  1. Artbuc1

    Thread Starter New Member

    Jan 3, 2016
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    Got a solar powered garden light with white Led lights with single AA rechargeable 800mAh,1.2v battery. Will be using indoors where there is not enough light to recharge battery so I want to add an external power supply. I want to use a switched battery holder containing 2 AA 1.5 batteries. I will disable the solar charging circuit so it does not try to charge batteries when I have the lights turned on during daytime. Then I will wire the external battery supply in parallel with the original single battery holder so the power will be supplied to the LED lights through the circuit board. My concern is increasing the supply voltage from 1.2 to 3v. I do not have the technical specs for the lights but have read that white LED's typically take 3+ forward volts. My lights have four wires going to each one so I assume they are wired in parallel. do I have enough information to be confident the higher supply voltage will not damage the lights? Thanks.
     
  2. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    Wire the batteries in parallel and the light will consume the same amount of current that it did before. As long as you do not increase the total voltage, you will not decrease the life of the LED any more than with one battery.
     
  3. Artbuc1

    Thread Starter New Member

    Jan 3, 2016
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    Thanks for the quick response! I assume the battery holder I have ordered will come with series wiring giving the 3VDC output. You are telling me to modify the holder so the two batteries will be in parallel delivering only 1.5VDC, right? I assume the 2 battery holder is still a good idea because the batteries will last twice as long, right? Thanks again.
     
  4. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    Yes rewire it so the batteries are in parallel.
     
  5. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    I am not understanding what your are try to do ..In the op you said that your are hooking up a external power supply to the AA batteries ???
    Maybe someone can hop in and please explain ..
     
  6. spinnaker

    AAC Fanatic!

    Oct 29, 2009
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    I think the OP just wants to increase the time the light can be lit.
     
  7. Dr.killjoy

    Well-Known Member

    Apr 28, 2013
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    Wouldn't it be easier to make a led driver with simply latching circuit if using a external power supply ??\
     
  8. Artbuc1

    Thread Starter New Member

    Jan 3, 2016
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    We are going to use the ornament inside where the solar panel will not get enough light to recharge the battery but will produce enough current to prevent the light from coming during early evenings and mornings when we want the lights on. I could just disable the charging circuit and put a single AA battery in the original holder and use the original switch, but it is a PITA to replace the battery and get to the switch. An external switched battery holder will make it much easier to replace batteries and switch lights on/off. The extra benefit is having two batteries which will allow longer run time but that is not my primary objective. I would have bought a single AA switched battery holder if I could have found one. My concern was applying 3VDC instead of 1.2VDC. Wiring the two external batteries in parallel will drop applied voltage to 1.5VDC which hopefully will be ok with white LED lights.
     
  9. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    The solar lamp will use a pr4403 chip to boost the output voltage to 3V, also the leds will only work when the solar cell is not giving out a voltage, removing the cell will make the leds come on continuously, even if your charger is connected to the battery the leds will be on, you need to put the charger in place of the solar cell.


    https://www.google.co.uk/url?sa=t&r...id=279&usg=AFQjCNG2vii7DirP1_ktAcjtJGt1wsd1xg
     
    Last edited: Jan 3, 2016
  10. Artbuc1

    Thread Starter New Member

    Jan 3, 2016
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    "The solar lamp will use a pr4403 chip to boost the output voltage to 3V, also the leds will only work when the solar cell is not giving out a voltage, removing the cell will make the leds come on continuously, even if your charger is connected to the battery the leds will be on, you need to put the charger in place of the solar cell."

    My unit has a switch built into the control circuit which allows you to turn the light on/off as long as the solar panel is not supplying juice. The output voltage from my unit is not boosted to 3V. It is virtually the same as the input voltage.
     
  11. wayneh

    Expert

    Sep 9, 2010
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    The measured voltage will be the same as the battery, but it's pulsing up to ~3V to power the LED. I've used these things with a 3V supply and it worked fine. It probably will have a shorter life, but I never checked - I just wanted to see if it would work and it did. If you put 2 batteries in parallel, be sure to choose batteries that are closely matched, i.e. two cells from the same fresh package.

    I'd just cover the solar cell to disable it from shutting off the LED.
     
  12. Artbuc1

    Thread Starter New Member

    Jan 3, 2016
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    wayneh said:

    "I'd just cover the solar cell to disable it from shutting off the LED."

    Did that for a couple days but it was easier to snip a wire (easy to reconnect in the future) and use the switch...will be even easier when I get the external switched battery holder. I was wondering if my VOM could detect the 3V pulse. My IC is not the pr4403 but it may be a joule thief type circuit.
     
  13. wayneh

    Expert

    Sep 9, 2010
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    My (free) Harbor Freight meter shows only the time-averaged value, I suppose. I was truly perplexed for a while that I could measure 1.5V on the LED leads, and it was lit. Yet if I hooked a 1.5V battery directly to it, nothing.

    I'd be curious if someone could put one of these on an oscilloscope. I speculate that if you supply 3V, it doesn't boost to 6V and destroy the LED. I think once current flows in the LED, the voltage is more-or-less capped at Vf. The current may be limited by the internal resistance of the boost inductor and other factors. Just guessing.
     
  14. dl324

    Distinguished Member

    Mar 30, 2015
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    Changing the battery isn't an option?

    I have one of those lights in my garage for some outdoor cats that sleep in. I just change the battery every evening and put the weak battery in a charger.
     
  15. wayneh

    Expert

    Sep 9, 2010
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    Lol, one of my best chuckles of the day. We need a picture!
     
  16. Artbuc1

    Thread Starter New Member

    Jan 3, 2016
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    dl324 wrote:
    "Changing the battery isn't an option?"

    Yes, I have my Panasonic charger and rechargeable batteries on order. With my light you have to partially disassemble to replace the battery. Would be a royal PITA to do that everyday. Also hard to access switch. An external switched battery pack will make things much more convenient.
     
  17. Artbuc1

    Thread Starter New Member

    Jan 3, 2016
    9
    0
    wayneh said:

    "I'd be curious if someone could put one of these on an oscilloscope. I speculate that if you supply 3V, it doesn't boost to 6V and destroy the LED. I think once current flows in the LED, the voltage is more-or-less capped at Vf. The current may be limited by the internal resistance of the boost inductor and other factors. Just guessing."

    According to the pr4403 data sheet, supply voltage must not exceed 1.9 volts or the chip may not operate properly. My chip is not a pr4403 but it may be a Chinese knock-off performing the same function.
     
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